Formation of resistant corn starches induced by gamma-irradiation

Effect of gamma ray dose on granular and molecular structures of gamma ray-irradiated cassava starch and its application in bioplastics

In this study, the effect of gamma ray irradiation on the granular and molecular structures of cassava starch was examined. Cassava starch was irradiated with various gamma ray doses of 25, 50, 75, and 100 kGy. After irradiation, the starch turned yellow, but its granular morphological characteristics remained intact. However, the inner part and the 'Maltese cross' of the starch granules irradiated with 100 kGy were broken, and its crystallinity decreased considerably. The pH reduction (from 5.6 to 3.7) and carboxyl content increase (up to 0.38 %) confirmed the formation of carboxyl groups on the irradiated starch chains. Gamma ray irradiation caused glycosidic bond cleavages, resulting in shortened amylose chains and debranched amylopectin chains containing terminal carboxyl groups. The irradiated starches with different molecular weights have high potential for use in food and non-food applications, for example, in bioplastics. Thermoplastic-irradiated starch (TPIS) materials, and their blends with poly(lactic acid) (PLA) were prepared via extrusion. Both TPIS and PLA/TPIS blends exhibited considerably increased melt flow index values compared with those from the unirradiated starch at approximate increases of 420-2260% and 2-55%, respectively. The improved melt flow ability and reduced viscosity are advantages for some plastic conversion processes such as injection molding.

Recent Advances in Physical Processing Techniques to Enhance the Resistant Starch Content in Foods: A Review

The physical modification of starch to produce resistant starch (RS) is a viable strategy for the glycemic index (GI) lowering of foods and functionality improvement in starchy food products. RS cannot be digested in the small intestine but can be fermented in the colon to produce short-chain fatty acids rather than being broken down by human digestive enzymes into glucose. This provides major health advantages, like better blood sugar regulation, weight control, and a lower chance of chronic illnesses. This article provides a concise review of the recent developments in physical starch modification techniques, including annealing, extrusion, high-pressure processing, radiation, and heat-moisture treatment. Specifically, the focus of this paper is on the alteration of the crystalline structure of starch caused by the heat-moisture treatment and annealing and its impact on the resistance of starch to enzymatic hydrolysis, as well as the granular structure and molecular arrangement of starch caused by extrusion and high-pressure processing, and the depolymerization and crosslinking that results from radiation. The impacts of these alterations on starch's textural qualities, stability, and shelf life are also examined. This review demonstrates how physically modified resistant starch can be used as a flexible food ingredient with both functional and health benefits. These methods are economically and ecologically sustainable since they successfully raise the RS content and improve its functional characteristics without the need for chemical reagents. The thorough analysis of these methods and how they affect the structural characteristics and health advantages of RS emphasizes the material's potential as an essential component in the creation of functional foods that satisfy contemporary dietary and health requirements.

Recent progress in regulating starch digestibility using natural additives and sustainable processing operations

The development of a healthier and more sustainable food supply is a main concern of consumers, industry, governments, and international institutions. Foods containing high levels of rapidly digestible starches have been linked to a rise in the number of people suffering from diet-related chronic diseases. Consequently, there is interest in reducing the digestibility of starch to improve their healthiness. The ability of natural additives including proteins, dietary fibers, and polyphenols, and sustainable processing technologies such as high-intensity ultrasonic, pulsed electric field, non-thermal plasma, γ-ray irradiation that regulate reduce starch digestibility in foods are reviewed. The potential mechanisms of action, advantages, and disadvantages of each approach at inhibiting starch digestibility is highlighted. The potential for commercializing these technologies is discussed, and areas where further research are required are emphasized. Natural additives and sustainable processing operations can effectively reduce the digestibility of starch and inhibit postprandial sugar "spikes" in the bloodstream by adjusting the structural changes, which can be used to create healthier and more sustainable foods and have broad application prospects.

Ionizing and nonionizing radiations can change physicochemical, technofunctional, and nutritional attributes of starch

Challenges for the food/non-food applications of starch mostly arise from its low stability against severe processing conditions (i.e. elevated temperatures, pH variations, intense shear forces), inordinate retrogradability, as well as restricted applicability. These drawbacks have been addressed through the modification of starch. The escalating awareness of individuals toward the presumptive side effects of chemical modification approaches has engrossed the attention of scientists to the development of physical modification procedures. In this regard, starch treatment via ionizing (i.e. gamma, electron beam, and X-rays) and non-ionizing (microwave, radiofrequency, infrared, ultraviolet) radiations has been introduced as a potent physical strategy offering new outstanding attributes to the modified product. Ionizing radiations, through dose-dependent pathways, are able to provoke depolymerization or cross-linking/grafting reactions to the starch medium. While non-ionizing radiations could modify the starch attributes by changing the morphology/architecture of granules and inducing reorientation/rearrangement in the molecular order of starch amorphous/crystalline fractions.

Using the dominant mutation gene Ae1-5180 (amylose extender) to develop high-amylose maize

Maize amylose is a type of high value-added starch used for medical, food, and chemical applications. Mutations in the starch branching enzyme (SBEIIb), with recessive ae (amylose extender) and dominant Ae1-5180 alleles, are the primary way to improve maize endosperm amylose content (AC). However, studies on Ae1-5180 mutation are scarce, and its roles in starch synthesis and breeding potential are unclear. We found that the AC of the Ae1-5180 mutant was 47.23%, and its kernels were tarnished and glassy and are easily distinguished from those of the wild type (WT), indicating that the dominant mutant has the classical characteristics of the ae mutant. Starch granules of Ae1-5180 became smaller, and higher in amount with irregular shape. The degree of amylopectin polymerisation changed to induce an increase in starch thermal stability. Compared with WT, the activity of granule-bound starch synthase and starch synthase was higher in early stages and lower in later stages, and other starch synthesis enzymes decreased during kernel development in the Ae1-5180 mutant. We successfully developed a marker (mu406) for the assisted selection of 17 Ae1-5180 near isogenic lines (NILs) according to the position of insertion of the Mu1 transposon in the SBEIIb promoter of Ae1-5180. JH214/Ae1-5180, CANS-1/Ae1-5180, CA240/Ae1-5180, and Z1698/Ae1-5180 have high breeding application potential with their higher AC (> 40%) and their 100-kernel weight decreased to < 25% compared to respective recurrent parents. Therefore, using the dominant Ae1-5180 mutant as a donor can detect the kernel phenotype and AC of Ae1-5180-NILs in advance, thereby accelerating the high-amylose breeding process.

Supplementary Information

The online version contains supplementary material available at 10.1007/s11032-022-01323-7.

Physicochemical, Morphological, and Functional Properties of Starches Isolated from Avocado Seeds, a Potential Source for Resistant Starch

This study compared the physicochemical and functional properties of starches from eight cultivars of avocado seeds. Amylose content, morphology, crystalline structure, swelling power, solubility, thermal and pasting properties, and in vitro digestibility were investigated. The results revealed that the apparent amylose content of starches from avocado seeds varied with different varieties. Light microscopic and scanning electron microscopic examination demonstrated that the eight starches differed slightly in terms of morphology and granule size. The X-ray diffraction and Fourier transform infrared spectroscopy analyses showed that the crystal structure and chemical linkage of the avocado seed starches were similar. However, the pasting, water solubility, and thermal properties of the eight avocado seed starches differed. Importantly, all the starches had high resistant starch content (>60%), with the highest found in Hass seeds (77.83%). To conclude, starch from avocado seeds has a high potential for use in the production of resistant starch.

Physico-chemical properties and digestibility of native and citrate starches change in different ways by synchrotron radiation

The physico-chemical properties and digestibility of native and citrate cassava starches changed as a result of synchrotron radiation treatment. In this study, the native and citrate starch samples were exposed to radiation doses of 0.1, 0.4, 0.8 and 3.9 kGy. The granular morphology revealed that all samples were rupture and damage after radiation. As increasing radiation doses, the relative crystallinity as determined by WAXS and the ratio of 1047/1015 cm^-1 from FTIR result decreased while the degree of degradation and solubility increased for all samples. The swelling power of radiated native starches decreased with higher radiation doses indicating that the cross-linking of starch was induced by synchrotron radiation which was related to an increase in the resistant starch content. On the contrary, for radiated citrate samples, the FTIR peak at 1724 cm^-1 was observed. The ratio of 1724/2900 cm^-1 and total esterified citric acid did not change. The swelling and degree of di-esterification were reduced while the degree of mono-esterification increased with higher doses. It implied that the cross-linking by ester bonds was broken into mono-ester bonds. This work demonstrated that synchrotron radiation changed the physical and chemical properties of native and citrate starches in different ways.

Modification of starch composition, structure and properties through editing of TaSBEIIa in both winter and spring wheat varieties by CRISPR/Cas9

Foods high in amylose content and resistant starch (RS) offer great potential to improve human health and lower the risk of serious noninfectious diseases. Common wheat (Triticum aestivum L.) is a major staple food crop globally. However, the RS contents in the grains of modern wheat varieties are low. Here, we report the generation of high-amylose wheat through targeted mutagenesis of TaSBEIIa in a modern winter wheat cv Zhengmai 7698 (ZM) and a spring wheat cv Bobwhite by CRISPR/Cas9, respectively. We generated a series of transgene-free mutant lines either with partial or triple-null TasbeIIa alleles in ZM and Bobwhite, respectively. Analyses of starch composition, structure and properties revealed that the effects of partial or triple-null alleles were dosage dependent with triple-null lines demonstrated more profound impacts on starch composition, fine structures of amylopectin and physiochemical and nutritional properties. The flours of triple-null lines possessed significantly increased amylose, RS, protein and soluble pentosan contents which benefit human health. Baking quality analyses indicated that the high-amylose flours may be used as additives or for making cookies. Collectively, we successfully modified the starch composition, structure and properties through targeted mutagenesis of TaSBEIIa by CRISPR/Cas9 in both winter and spring wheat varieties and generated transgene-free high-amylose wheat. Our finding provides deep insights on the role of TaSBEIIa in determining starch composition, structure, properties and end-use quality in different genetic backgrounds and improving RS content with multiple breeding and end-use applications in cereal crop species through genome editing for health benefits.

Understanding the Properties of Starch in Potatoes (Solanum tuberosum var. Agria) after Being Treated with Pulsed Electric Field Processing

The purpose of this study was to investigate the properties of starch in potatoes (Solanum tuberosum cv. Agria) after being treated with pulsed electric fields (PEF). Potatoes were treated at 50 and 150 kJ/kg specific energies with various electric field strengths of 0, 0.5, 0.7, 0.9 and 1.1 kV/cm. Distilled water was used as the processing medium. Starches were isolated from potato tissue and from the PEF processing medium. To assess the starch properties, various methods were used, i.e., the birefringence capability using a polarised light microscopy, gelatinisation behaviour using hot-stage light microscopy and differential scanning calorimetry (DSC), thermal stability using thermogravimetry (TGA), enzyme susceptibility towards α-amylase and the extent of starch hydrolysis under in vitro simulated human digestion conditions. The findings showed that PEF did not change the properties of starch inside the potatoes, but it narrowed the temperature range of gelatinisation and reduced the digestibility of starch collected in the processing medium. Therefore, this study confirms that, when used as a processing aid for potato, PEF does not result in detrimental effects on the properties of potato starch.

Physicochemical, structural and functional properties of native and irradiated starch: a review

The world population has crossed seven billion and such a huge population has increased the pressure and considerably affects our ability to feed ourselves. It has now emerged as a new challenge for policy makers, food scientists and other associated people to make food available to everyone. To achieve this, underutilized crops/plants that act as good sources of starch need to be explored. Starch in its native form have certain limitations in its functional properties to be used for different applications. Therefore, it becomes important to explore certain technologies which could be used for modification of properties of starch. During the last decades gamma irradiation has emerged as an efficient processing technique for the modification of starch when compared to the other available processes. This review, aims to summarize the effects of gamma irradiation on various properties of starch such as physicochemical and rheological properties, functional characteristics, thermal behaviour etc. so as to make the starch suitable for various applications in different industries including the food industry.

Alternative splicing results in a lack of starch synthase IIa-D in Chinese wheat landrace

We evaluated the SGP-1 protein composition of 368 Chinese wheat landraces using SDS-PAGE. The SGP-D1 null type was identified in three accessions (Xiaoqingmang, Pushanbamai, and P119). An 18-bp deletion and 9-bp variation were found at the junction region of the 7th intron and 8th exon, leading to deletion of the intron-exon junction recognition site AG when aligned the 8261-bp DNA sequence of TaSSIIa-D in Pushanbamai with that of Chinese Spring. Four cDNA types with mis-spliced isoforms were subsequently detected through amplification of TaSSIIa-D cDNAs. Among these, nine type II cDNAs with a 16-bp deletion in the 8th exon were detected, indicating that the major transcriptional pattern of TaSSIIa in Pushanbamai is type II. In the type IV cDNA, a 97-bp sequence remains undeleted in the end of the 5th exon. The amylose content in Pushanbamai was significantly higher than that in all control lines under field conditions, which suggested that deletion of SGP-D1 has an efficient impact on amylose content. As the TaSSIIa gene plays an important role in regulating the content of amylose, it is anticipated that these natural variants of TaSSIIa-D will provide useful resources for quality improvement in wheat.

Effects of electron beam irradiation on physicochemical properties of corn flour and improvement of the gelatinization inhibition

The properties and viscosity-reduction mechanism of corn flour irradiated by electron beam have not been understood properly. Here, we investigate the effects of electron beam irradiation (EBI) on the gelatinization and physicochemical properties of corn flour irradiated by 0-5.40kGy of electron beam. The total starch and crude fiber contents of corn flour decreased significantly (P<0.05) after EBI treatment, while the moisture and reducing sugar contents increased significantly (P<0.05). EBI caused perforations on the corn flour particle surfaces, and the irradiated parts of the particles would gradually peel off and afford smooth surfaces, spherical structures, and smaller sizes. Molecular chains of corn flour broke owing to EBI. After irradiation, the pasting peak viscosity decreased dramatically (P<0.01) from 1251.74 to 7.16Pa·s, showing that the gelatinization of corn flour was completely inhibited. Thus, EBI can be used to inhibit the gelatinization of corn flour, which may be beneficial for industrial and food formulations.

A genetic strategy generating wheat with very high amylose content

Resistant starch (RS), a type of dietary fibre, plays an important role in human health; however, the content of RS in most modern processed starchy foods is low. Cereal starch, when structurally manipulated through a modified starch biosynthetic pathway to greatly increase the amylose content, could be an important food source of RS. Transgenic studies have previously revealed the requirement of simultaneous down-regulation of two starch branching enzyme (SBE) II isoforms both located on the long arm of chromosome 2, namely SBEIIa and SBEIIb, to elevate the amylose content in wheat from ~25% to ~75%. The current study revealed close proximity of genes encoding SBEIIa and SBEIIb isoforms in wheat with a genetic distance of 0.5 cM on chromosome 2B. A series of deletion and single nucleotide polymorphism (SNP) loss of function alleles in SBEIIa, SBEIIb or both was isolated from two different wheat populations. A breeding strategy to combine deletions and SNPs generated wheat genotypes with altered expression levels of SBEIIa and SBEIIb, elevating the amylose content to an unprecedented ~85%, with a marked concomitant increase in RS content. Biochemical assays were used to confirm the complete absence in the grain of expression of SBEIIa from all three genomes in combination with the absence of SBEIIb from one of the genomes.

Gamma irradiation of corn starches with different amylose-to-amylopectin ratio

Corn starches with different amylose-to-amylopectin ratio (waxy, normal, Hylon V, and Hylon VII) were treated with five doses of gamma irradiation (1, 5, 10, 25, and 50 kGy). The effects of gamma irradiation on the physicochemical properties of starch samples were investigated. Waxy samples showed an increase of amylose-like fractions when irradiated at 10 kGy. The reduction in apparent amylose content increased with amylose content when underwent irradiation at 25 and 50 kGy. Low amylose starches lost their pasting ability when irradiated at 25 and 50 kGy. Results from thermal behavior and pasting profile suggested that low level of cross-linking occurred in Hylon VII samples irradiated at 5 kGy. Severe reduction in pasting properties, gelatinization temperatures and relative crystallinity with increasing irradiation intensity revealed that waxy samples were affected more by gamma irradiation; this also indicated amylopectin was the starch fraction most affected by gamma irradiation. Alteration level was portrayed differently when different kind of physicochemical properties were investigated, in which the pasting properties and crystallinity of starches were more immensely influenced by gamma irradiation while thermal behavior was less affected. Despite the irradiation level, the morphology and crystal pattern of starch granules were found remain unchanged by irradiation.